Filter using film bulk acoustic resonator and transmission/reception switch

ABSTRACT

A transmission band filter ( 110 ) having a series of elements ( 111, 113, 115 ) each composed of a film bulk acoustic resonator and grounded shunt elements ( 112, 114 ) each composed of a film bulk acoustic resonator is connected between a transmission port ( 102 ) and an antenna port ( 106 ). A reception band filter ( 130 ) having a series of elements ( 131, 133, 135 ) each composed of a film bulk acoustic resonator and grounded shunt elements ( 132, 134, 136 ) each composed of a film bulk acoustic resonator is connected between a reception port ( 104 ) and the antenna port ( 106 ). A film bulk acoustic resonator ( 150 ) for adjustment is connected between the antenna port ( 106 ) and the ground. The resonance frequency of the adjusting film bulk acoustic resonator ( 150 ) lies between the upper limit frequency of the transmission frequency pass band of the transmission band filter ( 110 ) and the lower limit frequency of the reception frequency pass band of the reception band filter ( 130 ). Therefore a duplexer such that it can be a monolithic element, the power handling capability is good, the size is small, and the cost is low is provided.

TECHNICAL FIELD

[0001] The present invention relates to a technical field of acommunication apparatus, particularly to a filter and duplexer using afilm bulk acoustic resonator.

BACKGROUND ART

[0002] There has constantly been a demand for miniaturization in an RFcircuit portion of a cellular phone. In recent years, there has been ademand for various functions to be imparted to the cellular phone. Torealize this, as many components as possible are preferablyincorporated. On the other hand, since a size of the cellular phone isrestricted, after all it is necessary to raise a mounting density in anapparatus. Therefore, a demand for reduction of an occupying area(mounting area) and height is strict particularly with respect to the RFcircuit portion. Therefore, the occupying area and the height have beenrequested to be reduced even with respect to the components constitutingthe RF circuit portion. Moreover, each component has been requested tobe constituted of a single part if possible, so that the portion can bemanufactured at a low cost. Especially concerning a duplexer ortransmission/reception switch which is one of the componentsconstituting the RF circuit portion, sufficient power handlingcapability is required, and it is necessary not to cause destruction andcharacteristic deterioration with respect to power supply.

[0003] At present, for the duplexer, a ceramic filter or a surfaceacoustic wave (SAW) filter has been used. The ceramic filter can bemonolithic and is inexpensive, but a loss of a resonator is large. Tocover this, a dimension of about 23×7×5 mm is required, and the demandfor the reduction of the mounting area or height cannot sufficiently besatisfied. On the other hand, the SAW filter is small in size, but has aproblem in the power handling capability at a high frequency, and thereis a possibility that the filter breaks down, when a surge is generatedin an output power of transmission. Moreover, in order to improvecharacteristics, a circuit also using an electronic switch can also beconstituted. However, in this case, the circuit constitution becomescomplicated and expensive.

[0004] In consideration of these situations, in JP(A) 2001-24476, aduplexer is proposed in which separation between a transmission band andreception band is little, and use in applications such as CDMA-PCSdevices requiring a higher power level is possible. The duplexer isconstituted of three components including a band filter fortransmission, band filter for reception, and 90-degrees phase shifter. Afilm bulk acoustic resonator (abbreviated as “FBAR”) constituting eachfilter has a very small size and high performance. However, the90-degrees phase shifter is other than the film bulk acoustic resonatorconstituting each filter, and is constituted of passive components suchas an inductor and capacitor. Therefore, for the duplexer described inthe above JP(A) 2001-24476, a plurality of filters and 90-degrees phaseshifter need to be mounted on one substrate, and it is difficult toconstitute a monolithic structure and to sufficiently reduce the cost.It is also possible to form the 90-degrees phase shifter of the duplexerby a transmission line. However, in this case, a length of at least tenor more millimeters is necessary, a considerably large space is requiredas compared with the filter, and this constitution is unsuitable forminiaturization. That is, features of the film bulk acoustic resonatorsuitable for the miniaturization cannot sufficiently be utilized.

[0005] Moreover, when the duplexer is used in the above-describedapplication, a pass band width of up to 4% of a central frequency isrequired in each filter (e.g., when the central frequency is 2 GHz, apass band width of about 80 MHz is required). However, a piezoelectricmaterial of the film bulk acoustic resonator for use in this applicationmainly contains AlN and ZnO. In this case, the required pass band widthcannot easily be achieved. This is because the pass band width islimited by a piezoelectric coupling coefficient (K2) which is a materialparameter. As one method for solving this problem, in JP(A) 2001-244704,it has been proposed that by connection of an external inductor elementin series or in parallel to the film bulk acoustic resonator, a broadpass band width be obtained as if an effective K2 of the materialincreased. However, this method has a defect that the inductor isattached to the film bulk acoustic resonator from the outside andaccordingly the whole size of the filter increases.

[0006] The present invention has been developed in consideration of theabove-described situation, and an object thereof is to provide aduplexer in which a connection portion between a filter for transmissionand a filter for reception can be structured to be small in size andwhich can be formed to be monolithic with the filter for transmissionand the filter for reception and which is satisfactory in power handlingcapability and small in size and inexpensive.

[0007] Moreover, the present invention has been developed inconsideration of the above-described situation, and an object thereof isto provide a duplexer in which a matching circuit for connecting afilter for transmission using a film bulk acoustic resonator to a filterfor reception using the film bulk acoustic resonator or passive elementssuch as an inductor for obtaining a useful pass band width of eachfilter are formed to be monolithic with the filters for transmission andreception and which is accordingly small in size and satisfactory inpower handling capability and easy to manufacture and can be reduced incost.

[0008] Furthermore, an object of the present invention is to provide afilter for use in the above-described duplexer.

DISCLOSURE OF THE INVENTION

[0009] In order to achieve the foregoing object, there is provided aduplexer comprising:

[0010] a transmission port, reception port, and transmission/receptionport;

[0011] a transmission band filter which is connected between thetransmission port and transmission/reception port and which includes afirst ladder-type circuit including a first series element constitutedof a film bulk acoustic resonator and a first shunt element constitutedof a film bulk acoustic resonator and which has a transmission frequencypass band; and

[0012] a reception band filter which is connected between the receptionport and transmission/reception port and which includes a secondladder-type circuit including a second series element constituted of afilm bulk acoustic resonator and a second shunt element constituted of afilm bulk acoustic resonator and which has a reception frequency passband not overlapped with the transmission frequency pass band,

[0013] wherein at least one film bulk acoustic resonator for adjustmentis connected between the port for transmission/reception and the firstand second shunt elements, and a resonance frequency of the film bulkacoustic resonator for adjustment is set between the transmissionfrequency pass band and the reception frequency pass band.

[0014] In an aspect of the present invention, the film bulk acousticresonator for adjustment is connected between the port fortransmission/reception and a ground, and the first and second shuntelements are connected to the ground.

[0015] In an aspect of the present invention, the transmission frequencypass band is set to be lower than the reception frequency pass band, andthe resonance frequency of the film bulk acoustic resonator foradjustment is set to a value between an upper limit frequency of thetransmission frequency pass band and a lower limit frequency of thereception frequency pass band.

[0016] In an aspect of the present invention, the transmission bandfilter includes at least one inductor for enhancing attenuationcharacteristics on a higher frequency side than the transmissionfrequency pass band. In an aspect of the present invention, the inductoris connected in parallel with same of the first series elements. In anaspect of the present invention, one end of the inductor is connected tothe transmission port.

[0017] In an aspect of the present invention, the reception band filterincludes at least one capacitor for enhancing attenuationcharacteristics on a lower frequency side than the reception frequencypass band. In an aspect of the present invention, the capacitor isconnected in parallel with some of the second series elements. In anaspect of the present invention, one end of the capacitor is connectedto the reception port.

[0018] In order to achieve the foregoing object, there is provided aduplexer comprising:

[0019] a transmission port, reception port, and transmission/receptionport;

[0020] a transmission band filter which is connected between thetransmission port and transmission/reception port and which includes afirst circuit including a first series element constituted of a filmbulk acoustic resonator and a first shunt element constituted of a filmbulk acoustic resonator and which has a transmission frequency passband; and

[0021] a reception band filter which is connected between the receptionport and transmission/reception port and which includes a second circuitincluding a second series element constituted of a film bulk acousticresonator and a second shunt element constituted of a film bulk acousticresonator and which has a reception frequency pass band,

[0022] wherein the transmission port, reception port,transmission/reception port, transmission band filter, and receptionband filter are formed using a common substrate, the substrate is aceramic substrate and includes a patterned conductive film in at leastan inner part, and a phase matching circuit formed using the patternedconductive film and connected to the port for transmission/reception,transmission band filter and reception band filter is disposed on thesubstrate.

[0023] In an aspect of the present invention, the phase matching circuitis formed using a conductive film having a line pattern shape whoselength extending to a connection end to the transmission band filterfrom that to the port for transmission/reception and whose lengthextending to a connection end to the reception band filter from that tothe port for transmission/reception are set to required values. In anaspect of the present invention, the phase matching circuit is formedusing at least one of a transmission side portion including an inductorand capacitor disposed between the port for transmission/reception andthe transmission band filter, and a reception side portion including aninductor and capacitor disposed between the port fortransmission/reception and the reception band filter. In an aspect ofthe present invention, the transmission band filter or the receptionband filter contains a passive element formed on the substrate includingthe patterned conductive film.

[0024] In an aspect of the present invention, the passive element is aninductor connected in series with the first shunt element of the firstcircuit or the second shunt element of the second circuit, an inductorconnected in parallel with the first series element of the firstcircuit, or a capacitor connected in parallel with the second serieselement of the second circuit.

[0025] In order to achieve the foregoing object, there is provided afilter connected between a first port and a second port, the filtercomprising: a series element constituted of a film bulk acousticresonator; and a shunt element constituted of a film bulk acousticresonator, the first and second ports, the series element, and the shuntelement being formed using a common substrate, the substrate being aceramic substrate including a patterned conductive film in at least aninner part, the substrate comprising a passive element formed using thepatterned conductive film and connected to the series element or theshunt element.

[0026] In an aspect of the present invention, the passive element is aninductor connected in series with the shunt element, an inductorconnected in parallel with the series element, or a capacitor connectedin parallel with the series element.

[0027] The ceramic substrate may be made of a laminate including aplurality of ceramic sheets and the patterned conductive film. Theceramic substrate may contain a mixture of ceramic and glass, and asintering temperature of the ceramic substrate may be in a range of 800to 950° C. The ceramic substrate may contain a mixture of alumina andborosilicate-based glass, a mixture of forsterite and borate-basedglass, or tin barium borate. The patterned conductive film may be madeof silver or copper.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a block diagram showing a constitution of a duplexer ofthe present invention;

[0029]FIG. 2 is a circuit constitution diagram of the duplexer of thepresent invention;

[0030]FIG. 3 is a schematic plan view of a film bulk acoustic resonator;

[0031]FIG. 4 is an X-X sectional view of FIG. 3;

[0032]FIG. 5 is a schematic sectional view of the film bulk acousticresonator;

[0033]FIG. 6 is an equivalent circuit diagram of the film bulk acousticresonator;

[0034]FIG. 7 is a graph showing one example of transmission andreception pass characteristics of the duplexer of the present invention;

[0035]FIG. 8 is a circuit constitution diagram of the duplexer of thepresent invention;

[0036]FIG. 9 is a block diagram showing a constitution of the duplexerof the present invention;

[0037]FIG. 10 is a circuit constitution diagram of the duplexer of thepresent invention;

[0038]FIGS. 11A, 11B, and 11C are circuit diagrams each showing anexample of a phase matching circuit;

[0039]FIG. 12 is a perspective view of the duplexer of the presentinvention;

[0040]FIG. 13 is a partial sectional view of FIG. 12;

[0041]FIGS. 14A and 14B are schematic perspective views each showing anexample of a passive element formed by a patterned conductive film in asubstrate;

[0042]FIG. 15 is a still another circuit constitution diagram of theduplexer of the present invention;

[0043]FIG. 16A is a diagram showing a configuration of an acousticresonator stack attached to a ceramic substrate; and

[0044]FIG. 16B is an X-X sectional view of FIG. 16A.

BEST MODE FOR CARRYING OUT THE INVENTION

[0045] Embodiments of the present invention will hereinafter bedescribed with reference to the drawings.

[0046]FIG. 1 is a block diagram showing a constitution of an embodimentof a duplexer or transmission/reception switch of the present invention.In FIG. 1, a duplexer 100 includes a transmission band filter 110,reception band filter 130, and film bulk acoustic resonator foradjustment 150. One end of the transmission band filter 110 is connectedto a first port (transmission port) 102, and one end of the receptionband filter 130 is connected to a second port (reception port) 104. Theother ends of the transmission band filter 110 and reception band filter130 are connected to a third port (antenna port which is a port both fortransmission and reception) 106. For the film bulk acoustic resonatorfor adjustment 150, one end thereof is connected to the antenna port 106(i.e., connected to the other ends of the transmission band filter 110and reception band filter 130), and the other end is connected to theground. The transmission port 102 is connected to a transmissioncircuit, the reception port 104 is connected to a reception circuit, andthe antenna port 106 is connected to a transmission/reception antennaANT.

[0047]FIG. 2 is a circuit constitution diagram of the duplexer 100 ofthe present embodiment. The film bulk acoustic resonator for adjustment150 is disposed to connect the transmission band filter 110 to thereception band filter 130. Either the transmission band filter 110 orthe reception band filter 130 includes a plurality of film bulk acousticresonators (FBARs).

[0048] Here, the film bulk acoustic resonator will briefly be described.

[0049]FIG. 3 is a schematic plan view of the film bulk acousticresonator, and FIG. 4 is an X-X sectional view thereof. A film bulkacoustic resonator 10 includes: a substrate 16 including a through-hole14 vertically extending between upper and lower surfaces to form an airgap; and a piezoelectric stack 22 configured such that a peripheral edgethereof is hung and supported on the upper surface of the substrate 16by an inner edge forming a through-hole opening in the upper surface ofthe substrate 16. The piezoelectric stack 22 includes a piezoelectriclayer 12 and electrode layers 18, 20 bonded to both the upper and lowersurfaces of the piezoelectric layer. Terminals 26, 28 are attached tothe electrode layers 18, 20, and the terminals 26, 28 are connected to apower supply. In the acoustic resonator stack 22, the piezoelectriclayer 12 expands and contracts in a direction shown by an arrow 24 inresponse to a voltage applied between the electrode terminals 26, 28.

[0050] The piezoelectric layer 12 contains piezoelectric materials whichcan be manufactured as a thin film, such as zinc oxide (ZnO) andaluminum nitride (AlN). The electrode layers 18, 20 is also be formed,for example, of gold (Au), molybdenum (Mo), or aluminum (Al). Thesubstrate 16 is formed of materials such as silicon (Si), SiO₂, GaAs,and glass.

[0051] The acoustic resonator stack 22 constituted of a laminate of thepiezoelectric layer 12 and electrode layers 18, 20 is hung in theperipheral edge thereof, and major surfaces both contact surroundinggases such as air or vacuum. In this case, the acoustic resonator stack22 forms an acoustic resonator high in Q. Alternating-current signalsapplied to the electrode layers 18, 20 via the terminals 26, 28 have afrequency which is equal to a value obtained by dividing the velocity ofsound in the acoustic resonator stack 22 by a double weighted thicknessof the stack 22. That is, in case of f_(r)=c/2t₀ (where f_(r) denotes aresonance frequency, c is the velocity of sound in the stack 22, and t₀denotes the weighted thickness of the stack 22), the acoustic resonatorstack 22 resonates in response to the alternating-current signal. Sincethe velocity of sound in the layer constituting the stack 22 differswith each material constituting each layer, the resonance frequency ofthe acoustic resonator stack 22 is determined not by a physicalthickness but by the weighted thickness in which the velocity of soundin the piezoelectric layer 12 or electrode layers 18, 20 and thephysical thicknesses of the layers are considered.

[0052]FIG. 5 is a schematic sectional view of the film bulk acousticresonator different from that of FIGS. 3 and 4. This example is the sameas that of FIGS. 3 and 4 except that an acoustic impedance converter 30is used instead of the air gap formed by the through-hole 14. This filmbulk acoustic resonator is described, for example, in a paper entitled“Face-Mounted Piezoelectric Resonators” by W. E. Newell (Proceedings ofthe IEEE, pp. 575 to 581, June 1965), and the like.

[0053]FIG. 6 shows an equivalent circuit of the film bulk acousticresonator 10 constituted as described above. Series resonance of theresonator occurs by an equivalent inductance (L_(m)) and equivalentcapacitance (C_(m)). Impedance of the resonator at series resonancefrequency is low (i.e., in an ideal case in which the device has noloss, this resonator functions like a shunt). At a frequency lower thanthe series resonance frequency, the impedance of the film bulk acousticresonator 10 has a capacitive property. At a frequency higher than theseries resonance frequency and lower than a frequency of parallelresonance generated from an equivalent capacitance (C₀), the impedanceof the film bulk acoustic resonator 10 has an inductive property.Moreover, at a frequency higher than the parallel resonance frequency,the impedance of the film bulk acoustic resonator 10 again has thecapacitive property. At the parallel resonance frequency, the impedanceof the resonator increases and, in an ideal system having no loss, theimpedance becomes infinite, and is similar to an open circuit. In thepresent invention, since changes of the impedance around the seriesresonance frequency with respect to the film bulk acoustic resonator foradjustment 150 are used, the constitution of the duplexer is formed tobe simple and small as described later.

[0054] For the individual resonators, the series resonance occurs by theequivalent inductance (L_(m)) and equivalent capacitance (C_(m)).Furthermore, by these and the equivalent capacitance (C₀), the parallelresonance occurs at the resonance frequency higher than that of theseries resonance.

[0055] The transmission band filter 110 and reception band filter 130will be described in further detail with reference to FIG. 2 again.

[0056] The transmission band filter 110 is a band filter of (2+½) stagesconnected so that series resonance elements 111, 113, 115 constituted ofthe film bulk acoustic resonators and shunt resonance elements 112, 114constituted of the film bulk acoustic resonators form a ladder-typecircuit. The ladder-type circuit is a general technique of using theacoustic resonator to constitute a band filter. The series resonanceelements 111, 113, 115 are connected between the first port(transmission port) 102 and the third port (antenna port) 106. The shuntresonance element 112 connects the ground to a node 117 between theseries resonance elements 111, 113. The shunt resonance element 114connects the ground to a node 118 between the series resonance elements113, 115.

[0057] The reception band filter 130 is a band filter of three stagesconnected so that series resonance elements 131, 133, 135 constituted ofthe film bulk acoustic resonators and shunt resonance elements 132, 134,136 constituted of the film bulk acoustic resonators form theladder-type circuit. The series resonance elements 131, 133, 135 areconnected between the second port (reception port) 104 and the thirdport (antenna port) 106. The shunt resonance element 132 connects theground to a node 137 between the series resonance elements 131, 133. Theshunt resonance element 134 connects the ground to a node 138 betweenthe series resonance elements 133, 135. The shunt resonance element 136connects the ground to the second port (reception port) 104.

[0058] One end of the film bulk acoustic resonator for adjustment 150 isconnected to the third port (i.e., connected to a connection portionbetween the series resonance element 111 of the transmission band filter110 and the series resonance element 131 of the reception band filter130), and the other end thereof is connected to the ground.

[0059] The film bulk acoustic resonator for adjustment 150 functions asa shunt resonator added to the ladder-type circuit of the transmissionband filter 110 in one aspect, and accordingly characteristics of thetransmission band filter of three stages are obtained. In a phone,usually a transmission frequency pass band is set to be lower than areception frequency pass band. For example, in a CDMA-PCS phone, thetransmission frequency pass band is 1.85 to 1.91 GHz, and the receptionfrequency pass band is 1.93 to 1.99 GHz. Therefore, for the transmissionband filter 110, a steep and large attenuation is required at afrequency higher than that of the pass band. When the characteristics ofthe transmission band filter of three stages are obtained, thecharacteristics substantially meet this requirement, and the duplexercan be miniaturized.

[0060] The film bulk acoustic resonator for adjustment 150 functions asthe shunt resonator added to the ladder-type circuit of the receptionband filter 130 in the other aspect, and accordingly the characteristicsof the reception band filter of (3+½) stages are obtained. For thereception band filter 130, the steep and large attenuation is requiredat a frequency lower than that of the pass band. When thecharacteristics of the reception band filter of (3+½) stages areobtained, the characteristics substantially meet this requirement, andthe duplexer can be miniaturized.

[0061] The series resonance frequency of the film bulk acousticresonator for adjustment 150 is set to an appropriate value which islarger than an upper limit value (1.91 GHz for the CDMA-PCS phone) ofthe transmission frequency pass band of the transmission band filter 110and smaller than a lower limit value (1.93 GHz for the CDMA-PCS phone)of the reception frequency pass band of the reception band filter 130.Accordingly, the duplexer 100 can be operated while the transmissionband filter 110 and reception band filter 130 are not mutuallyinfluenced. This is because the transmission frequency pass band islower than the series resonance frequency of the resonator 150, and theresonator 150 therefore shows the capacitive property in the circuit inthe transmission frequency pass band, and behaves by the function likeLPF as if the reception band filter 130 did not exist. Moreover, thereception frequency pass band is higher than the series resonancefrequency of the resonator 150, and the resonator 150 therefore showsthe inductive property in the circuit in the reception frequency passband, and behaves by the function like HPF as if the presence of thetransmission band filter 110 were ignored. Therefore, by the presence ofthe resonator 150, the transmission signal applied to the first port(transmission port) 102 flows to the third port (antenna port) 106 fromthe first port (transmission port) 102, and hardly influences the secondport (reception port) 104 or the reception band filter 130. Moreover, bythe presence of the resonator 150, the reception signal coming via thethird port (antenna port) 106 passes through the reception band filter130 to reach the second port (reception port) 104 without beinginfluenced by the transmission band filter 110 or the first port(transmission port) 102.

[0062]FIG. 7 shows one example of transmission pass characteristics Ttand reception pass characteristics Rt of the duplexer 100 including thefilm bulk acoustic resonator for adjustment 150 constituted as describedabove.

[0063] Since the film bulk acoustic resonator for adjustment 150 caneasily be constituted to be monolithic together with the film bulkacoustic resonators constituting the transmission band filter 110 andreception band filter 130, the duplexer can be miniaturized also in thismeaning.

[0064]FIG. 8 is a circuit constitution diagram of still anotherembodiment of the duplexer of the present invention. In the figure,members or parts having functions similar to those in FIGS. 1 to 7 aredenoted with the same reference numerals.

[0065] In the present embodiment, in the transmission band filter 110,the node 117 is connected to the first port (transmission port) 102 viaan inductor 120 which is an additional passive element. That is, theinductor 120 is connected in parallel with the series resonance elements113, 115. An additional resonance circuit is formed between theequivalent capacitance C₀ of each series resonance element and theinductor 120. Accordingly, a new attenuation pole is formed in a desiredattenuation band (especially a frequency close to the pass band andhigher than the pass band), and further better transmission filtercharacteristics can be obtained with a smaller number of stages.

[0066] Moreover, in the present embodiment, the node 137 is connected tothe second port 104 via a capacitor 140 which is an additional passiveelement. That is, the capacitor 140 is connected in parallel with theseries resonance elements 133, 135. The additional resonance circuit isformed between each series resonance element and the capacitor 140.Accordingly, the new attenuation pole is formed in the desiredattenuation band (especially a frequency close to the pass band andlower than the pass band), and further better reception filtercharacteristics can be obtained with the smaller number of stages.

[0067] It is to be noted that in the above-described embodiment one filmbulk acoustic resonator for adjustment 150 is used, but two or more filmbulk acoustic resonators for adjustment can also be used in the presentinvention.

[0068]FIG. 9 is a block diagram showing the constitution of theembodiment of the duplexer of the present invention. In FIG. 9, theduplexer 100 includes the transmission band filter 110, the receptionband filter 130, and a phase matching circuit 150. One end of thetransmission band filter 110 is connected to the first port(transmission port) 102, and one end of the reception band filter 130 isconnected to the second port (reception port) 104. The other ends of thetransmission band filter 110 and reception band filter 130 are connectedto the third port (antenna port which is the port both for transmissionand reception) 106 via the phase matching circuit 150. That is, thephase matching circuit 150 is connected to the antenna port 106,transmission band filter 110, and reception band filter 130,respectively. The transmission port 102 is connected to the transmissioncircuit, the reception port 104 is connected to the reception circuit,and the antenna port 106 is connected to the transmission/receptionantenna ANT.

[0069]FIG. 10 is a circuit constitution diagram of the duplexer 100 ofthe present embodiment. The phase matching circuit 150 is disposed toconnect the transmission band filter 110 to the reception band filter130. Either the transmission band filter 110 or the reception bandfilter 130 includes a plurality of film bulk acoustic resonators(FBARs).

[0070] The transmission band filter 110 and reception band filter 130will be described in further detail with reference to FIG. 10.

[0071] The transmission band filter 110 is a band filter of (2+½) stagesconnected so that the series resonance elements 111, 113, 115 which arefirst series elements constituted of the film bulk acoustic resonatorsand the shunt resonance elements 112, 114 which are first shunt elementsconstituted of the film bulk acoustic resonators form the ladder-typecircuit which is a first circuit. The ladder-type circuit is a generaltechnique of using the acoustic resonator to constitute the band filter.The series resonance elements 111, 113, 115 are connected between thefirst port (transmission port) 102 and the phase matching circuit 150.The shunt resonance element 112 connects the ground to the node 117between the series resonance elements 111, 113. The shunt resonanceelement 114 connects the ground to the node 118 between the seriesresonance elements 113, 115. It is to be noted that as shown an inductor119 is disposed between the shunt resonance element 114 and the ground.The inductor 119 also functions as a passive element for obtainingfilter characteristics close to desired characteristics (i.e., enhancingthe filter characteristics). When inductance of the inductor 119 isappropriately set, the pass band of the transmission band filter 110 canbe set substantially as desired.

[0072] The reception band filter 130 is a band filter of three stagesconnected so that the series resonance elements 131, 133, 135 which aresecond series elements constituted of the film bulk acoustic resonatorsand the shunt resonance elements 132, 134, 136 which are second shuntelements constituted of the film bulk acoustic resonators form theladder-type circuit which is a second circuit. The series resonanceelements 131, 133, 135 are connected between the second port (receptionport) 104 and the phase matching circuit 150. The shunt resonanceelement 132 connects the ground to the node 137 between the seriesresonance elements 131, 133. The shunt resonance element 134 connectsthe ground to the node 138 between the series resonance elements 133,135. The shunt resonance element 136 connects the ground to the secondport (reception port) 104. It is to be noted that, as shown, inductors139, 139′ are disposed between the shunt resonance elements 134, 136 andthe ground, respectively. The inductors 139, 139′ function as passiveelements for obtaining the filter characteristics substantially asdesired (i.e., enhancing the filter characteristics). When theinductances of the inductors 139, 139′ are appropriately set, the passband of the reception band filter 130 can be set substantially asdesired to be different from that of the transmission band filter 110.

[0073] The phase matching circuit 150 is connected to the third port(antenna port which is the port both for the transmission and reception)106, the series resonance element 111 of the transmission band filter110, and the series resonance element 131 of the reception band filter130, respectively. It is to be noted that in FIGS. 9 and 10 the phasematching circuit 150 is connected to the ground, but the phase matchingcircuit 150 does not have to be connected to the ground.

[0074]FIGS. 11A, 11B, and 11C are circuit diagrams showing an example ofthe phase matching circuit 150. In FIG. 11A, the phase matching circuit150 is formed using a transmission side portion including an inductor L1and capacitor C1 disposed between the antenna port 106 and transmissionband filter 110, and a reception side portion including an inductor L2and capacitor C2 disposed between the antenna port 106 and receptionband filter 130. In FIG. 11B, the phase matching circuit 150 is formedusing only the reception side portion including the inductors L1, L2 andcapacitor C disposed between the antenna port 106 and reception bandfilter 130. It is possible to form the phase matching circuit 150 usingonly the transmission side portion. In FIG. 11C, the phase matchingcircuit 150 is formed using a conductive film S1 having a line patternshape extending to a connection end to the transmission band filter 110from that to the antenna port 106, and a conductive film S2 having aline pattern shape extending to the connection end to the reception bandfilter 130 from that to the antenna port 106. Here, assuming that acentral frequency of the transmission band filter 110 is ft, the centralfrequency of the reception band filter 130 is fr, the light velocity isc, and an effective specific inductive capacity of the substrate 16 onwhich the conductive films S1, S2 are formed is εr, a length of theconductive film S1 is set to (λr/4)=c/[4{square root}{square root over ()}(εr)fr] and the length of the conductive film S2 is set to(λt/4)=c/[4{square root}{square root over ( )}(εr)ft]. λt, λr denotewavelengths corresponding to the frequencies ft, fr, respectively.

[0075] By the presence of the appropriately set phase matching circuit150, the transmission signal applied to the first port (transmissionport) 102 flows to the third port (antenna port) 106 from the first port(transmission port) 102, and hardly influences the second port(reception port) 104 or the reception band filter 130. Moreover, by thepresence of the phase matching circuit 150, the reception signal comingvia the third port (antenna port) 106 passes through the reception bandfilter 130 to reach the second port (reception port) 104 without beinginfluenced by the transmission band filter 110 or the first port(transmission port) 102. Therefore, the circuit steadily functions asthe duplexer.

[0076]FIG. 12 is a perspective view of the duplexer, and FIG. 13 is apartial sectional view of the duplexer. The substrate 16 is a ceramicsubstrate. As shown in FIG. 13, the ceramic substrate 16 is made of alaminate including a plurality of ceramic sheets 16 a-1, 16 a-2, 16 a-3,16 a-4 and patterned conductive films 16 b positioned between theceramic sheets disposed adjacent to each other. The ceramic sheet isformed, for example, of a mixture of ceramic and glass. Alternatively,the ceramic sheet is formed, for example, of a mixture of alumina andborosilicate-based glass, a mixture of forsterite and borate-basedglass, or tin barium borate. Moreover, the conductive films 16 b areformed, for example, of silver or copper high in conductivity. For thelaminate of the ceramic sheet and patterned conductive film, a silver orcopper paste is applied in a desired pattern between adjacent ceramicgreen sheets among a plurality of ceramic green sheets, and sintered at800 to 950° C. which is a relatively low temperature so that thelaminate can easily be obtained. Through-holes are formed in appropriatepositions in the ceramic sheet, and the patterned conductive film 16 bis connected to another film of the adjacent layer via a through-holeconductor 16 c charged in the through-hole.

[0077] The thickness of the ceramic substrate 16 is, for example, 0.5 to1.2 mm, that of each of the ceramic sheets 16 a-1, 16 a-2, 16 a-3, 16a-4 is, for example, 0.02 to 0.3 mm, and that of the patternedconductive film 16 b is, for example, 0.005 to 0.02 mm. It is to benoted that only a required number of ceramic sheets for forming adesired circuit element by the patterned conductive films 16 b may beused.

[0078] In the ceramic substrate 16, the materials of the ceramic sheetsdisposed adjacent to each other may be either different or the same.When the materials of the adjacent ceramic sheets are the same, theindividual sheets cannot be distinguished in some case. Even in such acase, the substrate is included in the ceramic substrate mentioned inthe present invention.

[0079]FIGS. 14A and 14B are schematic perspective views showing anexample of a passive element formed by the patterned conductive film 16b in the substrate 16. FIG. 14A shows the inductor, and the inductor isformed in a spiral pattern LP in the same plane. The spiral pattern mayalso be connected to that of the adjacent layer via the through-holeconductor in a through-hole TH formed in the ceramic sheet. FIG. 14Bshows a capacitor, and the capacitor is constituted of planar electrodesCP1, CP2 of two layers disposed adjacent to each other.

[0080] In FIG. 13, the phase matching circuit 150 of FIG. 11A describedabove is formed in the substrate 16, and further the inductors 119, 139,139′ are formed. On the upper surface of the substrate 16, the resonanceelements 111, 114, etc. constituting the transmission band filter 110and the resonance elements 131, 134, 136, etc. constituting thereception band filter 130 are disposed. To cover these resonanceelements, on the upper surface of the substrate 16, a cover member 110 aon the side of the transmission band filter and a cover member 130 a onthe side of the reception band filter are bonded. A ground conductivefilm G is attached to substantially the whole lower surface of thesubstrate 16.

[0081] As described above, the transmission port 102, reception port104, antenna port 106, transmission band filter 110, and reception bandfilter 130 are formed using the common substrate 16, and the substrate16 is constituted of the laminate including a plurality of ceramicsheets and patterned conductive films. Accordingly, the phase matchingcircuit 150 and further the inductors 119, 139, 139′ which are thepassive elements for enhancing the filter characteristics can be made inthe substrate 16. Therefore, the duplexer can be miniaturized usingadvantages resulting from the film bulk acoustic resonator of the smallsize. Moreover, since the patterned conductive film constituted of Ag,Cu high in conductivity can be used, and the capacitor or the inductorhigh in Q value can be constituted, the small-sized duplexer can beconstituted without substantially deteriorating the filtercharacteristics.

[0082]FIGS. 16A and 16B are diagrams showing still another embodiment ofthe attachment of the acoustic resonator stack with respect to theceramic substrate, wherein FIG. 16A shows a schematic plan view, andFIG. 16B shows an X-X sectional view thereof. A concave portion 14′ isformed below the acoustic resonator stack 22 in the upper surface of theceramic substrate 16. The concave portion 14′ has a depth to such anextent that vibration of the acoustic resonator stack 22 in a verticaldirection is permitted, and the depth is, for example, about severalmicrons. The concave portion 14′ is formed in the substrate materialbefore sintering, the concave portion 14′ is filled with a syntheticresin after the sintering, the acoustic resonator stack 22 is formed onthe portion, and the synthetic resin in the concave portion 14′ isremoved. Accordingly, the configuration of FIGS. 16A and 16B can beobtained. The acoustic resonator stack 22 may be formed on a filmbeforehand, and fixed to the ceramic substrate 16 by using metal bumpssuch as solder balls with a space interposed therebetween.

[0083]FIG. 15 is a circuit constitution diagram of a still anotherembodiment of the duplexer of the present invention. In the figure, themembers or parts having the functions similar to those in FIGS. 1 to 14are denoted with the same reference numerals.

[0084] In the present embodiment, in the transmission band filter 110,the node 117 is connected to the first port (transmission port) 102 viathe inductor 120 which is the additional passive element. That is, theinductor 120 is connected in parallel with the series resonance elements113, 115. The additional resonance circuit is formed between theequivalent capacitance Co of each series resonance element and theinductor 120. Accordingly, the new attenuation pole is formed in thedesired attenuation band (especially the frequency close to the passband and higher than the pass band), and further better transmissionfilter characteristics can be obtained with the smaller number ofstages.

[0085] Moreover, in the present embodiment, the node 137 is connected tothe second port (reception port) 104 via the capacitor 140 which is theadditional passive element. That is, the capacitor 140 is connected inparallel with the series resonance elements 133, 135. The additionalresonance circuit is formed between each series resonance element andthe capacitor 140. Accordingly, the new attenuation pole is formed inthe desired attenuation band (especially the frequency close to the passband and lower than the pass band), and further better reception filtercharacteristics can be obtained with the smaller number of stages.

[0086] It is to be noted that in-the above-described embodiment onephase matching circuit 150 is used, but two or more phase matchingcircuits can also be used in the present invention.

[0087] Industrial Applicability

[0088] As described above, according to the present invention, anelement constituted of a film bulk acoustic resonator is used, andtherefore it is possible to provide a duplexer whose reliability orstability of filter characteristics is not impaired even at a powerlevel exceeding 1 watt and which has sufficiently steep attenuationcharacteristics. There can also be provided a duplexer which isconsiderably small in size and height as compared with a ceramic filter.Since the film bulk acoustic resonator for adjustment is used even inconnecting a transmission band filter to a reception band filter, amonolithic element is easily constituted, and a manufacturing cost ofthe duplexer can be reduced.

[0089] Moreover, as described above, according to the duplexer of thepresent invention, the transmission port, reception port, port for boththe transmission and reception, the transmission band filter includingfilm bulk acoustic resonator, and the reception band filter includingthe film bulk acoustic resonator are formed using the common ceramicsubstrate including the patterned conductive film. In the ceramicsubstrate, the patterned conductive film is used to form the phasematching circuit, and therefore miniaturization, enhancement of powerhandling capability, facilitation of manufacturing, and cost reductionare possible.

[0090] Furthermore, according to the filter of the present invention,the series element constituted of the film bulk acoustic resonator andthe shunt element constituted of the film bulk acoustic resonator areformed using the common ceramic substrate including the patternedconductive film together with first and second ports, and the passiveelement is disposed using the patterned conductive film in the ceramicsubstrate, so that the miniaturization, enhancement of the powerhandling capability, facilitation of the manufacturing, and costreduction are possible.

1. A duplexer comprising: a transmission port, reception port, andtransmission/reception port; a transmission band filter which isconnected between the transmission port and transmission/reception portand which includes a first ladder-type circuit including a first serieselement constituted of a film bulk acoustic resonator and a first shuntelement constituted of a film bulk acoustic resonator and which has atransmission frequency pass band; and a reception band filter which isconnected between the reception port and transmission/reception port andwhich includes a second ladder-type circuit including a second serieselement constituted of a film bulk acoustic resonator and a second shuntelement constituted of a film bulk acoustic resonator and which has areception frequency pass band not overlapped with the transmissionfrequency pass band, wherein at least one film bulk acoustic resonatorfor adjustment is connected between the port for transmission/receptionand the first and second shunt elements, and a resonance frequency ofthe film bulk acoustic resonator for adjustment is set between thetransmission frequency pass band and the reception frequency pass band.2. The duplexer according to claim 1, wherein the film bulk acousticresonator for adjustment is connected between the port fortransmission/reception and a ground, and the first and second shuntelements are connected to the ground.
 3. The duplexer according to claim1, wherein the transmission frequency pass band is set to be lower thanthe reception frequency pass band, and the resonance frequency of thefilm bulk acoustic resonator for adjustment is set to a value between anupper limit frequency of the transmission frequency pass band and alower limit frequency of the reception frequency pass band.
 4. Theduplexer according to claim 3, wherein the transmission band filterincludes at least one inductor for enhancing attenuation characteristicson a higher frequency side than the transmission frequency pass band. 5.The duplexer according to claim 4, wherein the inductor is connected inparallel with some of the first series elements.
 6. The duplexeraccording to claim 5, wherein one end of the inductor is connected tothe transmission port.
 7. The duplexer according to claim 3, wherein thereception band filter includes at least one capacitor for enhancingattenuation characteristics on a lower frequency side than the receptionfrequency pass band.
 8. The duplexer according to claim 7, wherein thecapacitor is connected in parallel with some of the second serieselements.
 9. The duplexer according to claim 8, wherein one end of thecapacitor is connected to the reception port.
 10. A duplexer comprising:a transmission port, reception port, and transmission/reception port; atransmission band filter which is connected between the transmissionport and transmission/reception port and which includes a first circuitincluding a first series element constituted of a film bulk acousticresonator and a first shunt element constituted of a film bulk acousticresonator and which has a transmission frequency pass band; and areception band filter which is connected between the reception port andtransmission/reception port and which includes a second circuitincluding a second series element constituted of a film bulk acousticresonator and a second shunt element constituted of a film bulk acousticresonator and which has a reception frequency pass band, wherein thetransmission port, reception port, transmission/reception port,transmission band filter, and reception band filter are formed using acommon substrate, the substrate is a ceramic substrate and includes apatterned conductive film in at least an inner part, and a phasematching circuit formed using the patterned conductive film andconnected to the port for transmission/reception, transmission bandfilter and reception band filter is disposed on the substrate.
 11. Theduplexer according to claim 10, wherein the ceramic substrate is made ofa laminate including a plurality of ceramic sheets and the patternedconductive film.
 12. The duplexer according to claim 10, wherein theceramic substrate contains a mixture of ceramic and glass, and asintering temperature of the ceramic substrate is in a range of 800 to950° C.
 13. The duplexer according to claim 10, wherein the ceramicsubstrate contains a mixture of alumina and borosilicate-based glass, amixture of forsterite and borate-based glass, or tin barium borate. 14.The duplexer according to claim 10, wherein the patterned conductivefilm is made of silver or copper.
 15. The duplexer according to claim10, wherein the phase matching circuit is formed using a conductive filmhaving a line pattern shape whose length extending to a connection endto the transmission band filter from that to the port fortransmission/reception and whose length extending to a connection end tothe reception band filter from that to the port fortransmission/reception are set to required values.
 16. The duplexeraccording to claim 10, wherein the phase matching circuit is formedusing at least one of a transmission side portion including an inductorand capacitor disposed between the port for transmission/reception andthe transmission band filter, and a reception side portion including aninductor and capacitor disposed between the port fortransmission/reception and the reception band filter.
 17. The duplexeraccording to claim 10, wherein the transmission band filter or thereception band filter contains a passive element formed on the substrateusing the patterned conductive film.
 18. The duplexer according to claim17, wherein the passive element is an inductor connected in series withthe first shunt element of the first circuit or the second shunt elementof the second circuit, an inductor connected in parallel with the firstseries element of the first circuit, or a capacitor connected inparallel with the second series element of the second circuit.
 19. Afilter which is used as the transmission band filter or the receptionband filter in the duplexer according to claim
 17. 20. A filterconnected between a first port and a second port, the filter comprising:a series element constituted of a film bulk acoustic resonator; and ashunt element constituted of a film bulk acoustic resonator, the firstand second ports, the series element, and the shunt element being formedusing a common substrate, the substrate being a ceramic substrateincluding a patterned conductive film in at least an inner part, thesubstrate comprising a passive element formed using the patternedconductive film and connected to the series element or the shuntelement.
 21. The filter according to claim 20, wherein the ceramicsubstrate is made of a laminate including a plurality of ceramic sheetsand the patterned conductive film.
 22. The filter according to claim 20,wherein the ceramic substrate contains a mixture of ceramic and glass,and a sintering temperature of the ceramic substrate is in a range of800 to 950° C.
 23. The filter according to claim 20, wherein the ceramicsubstrate contains a mixture of alumina and borosilicate-based glass, amixture of forsterite and borate-based glass, or tin barium borate. 24.The filter according to claim 20, wherein the patterned conductive filmis made of silver or copper.
 25. The filter according to claim 20,wherein the passive element is an inductor connected in series with theshunt element, an inductor connected in parallel with the serieselement, or a capacitor connected in parallel with the series element.